Scientists from the Technical Research Centre of Finland (VTT) investigated the capabilities of various prebiotic fibres to protect the stability and viability of probiotic Lactobacillus rhamnosus strains during freeze-drying, storage in freeze-dried form and after formulation into apple juice and chocolate-coated breakfast cereals.
"The present study indicated that some fibre preparations have the potential in technological applications in protecting probiotic viability and stability during processing and storage in food matrices," wrote lead author Maria Saarela in the International Journal of Food Microbiology.
"Currently food products combining probiotics with prebiotics or fibres are gaining more interest and are introduced into the market. These kinds of products would attain added value if the fibre could protect probiotic cells during down-stream processing, formulation and/or storage and thus improve their viability and stability."
Most foods containing probiotic bacteria are found in the refrigerated section of supermarkets as the bacteria is destroyed by heat and other processing conditions.
This has given the dairy sector, already used to handling live bacteria for the manufacture of yoghurt, a major advantage in probiotic foods - probiotic drinking yoghurts are currently the fastest growing dairy product in Europe.
But increasing research has focused on expanding protecting probiotics during processing and expanding the food categories available to prebiotics. Such an avenue of research has led companies like Cell Biotech from Korea using a dual-coating to protect probiotics against oxygen, acid, moisture and high temperatures for use in emerging new product categories such as breakfast cereals and smoothies.
Maria Saarela told NutraIngredients.com that by choosing the right combination of pre- and probiotic the stability of the latter could be enhanced for a specific application.
"If the fibre effect is also wanted, then more of the same carrier substrate can be added directly into the product," she said.
Focussing on the L. rhamnosus strains E-97800 (E800) and E-94522 (E522) from VTT culture collection, probiotic-prebiotic pairs were prepared with a range of fibres, including oat flour (10 and 20 per cent beta-glucan, Natureal, Suomen Viljava Oy), apple fibre, wheat dextrin (Nutriose FB, Roquette), polydextrose (Litesse, Danisco) and inulin (Raftiline, Orafti).
"Skim milk supplemented with polydextrose has been used to spray-dry probiotics, but with fairly poor results (regarding the addition of polydextrose)," said Saarela. "Wheat dextrin and oat flour have not been studied before, as far as I know."
The VTT researchers report that different adhesion properties of the probiotic strains to the various fibre preparations, with the L. rhamnosus E800 found to be highly adherent, while E522 adhesion was relatively poor.
"Good adhesion to fibre preparations is not a common feature among lactic acid bacteria," said the researchers.
They also said that, of all the fibre carriers studied, wheat dextrin and polydextrose had the most potential as carriers for the L. rhamnosus strains for freeze-drying, with both survival and storage stability at 37 degrees Celsius reported to be comparable to the sucrose control carrier.
When incorporated into the chocolate-coated breakfast cereals, the researchers reported that wheat dextrin and polydextrose again proved to be better carriers.
However, when formulated into the low pH apple juice (pH3.5) the oat flour with 20 per cent beta-glucan showed the best potential for carriers of fresh probiotic cells during storage.
"Perhaps the main finding in this study was that different fibres can be used in different applications: polydextrose and dextrin were good freeze-drying carriers and for dry applications whereas oat rich in beta-glucan was a good carrier for fresh cells in apple juice," Saarela told this website.
The study was funded by the National Technology Agency of Finland, and as part of the European Commission's RTD programme, "Quality of Life and Management of Living Resources".
Source: International Journal of Food Microbiology November 2006, Volume 112, Issue 2, Pages 171-178 "Fibres as carriers for Lactobacillus rhamnosus during freeze-drying and storage in apple juice and chocolate-coated breakfast cereals"
Authors: M. Saarela, I. Virkajärvi, L. Nohynek, A. Vaari and J. Mättö